It is known that the echo canceller forms an echo replica signal by using an adaptive filter and removes an echo component from a near-end input signal by the echo replica signal. The echo canceller also causes the filter coefficient of an adaptive filter to be updated and to converge on a predetermined algorithm (e.g., LMS) to form an appropriate echo replica signal. A higher convergence speed of the filter coefficient is preferable because the time for forming an appropriate echo replica signal is reduced.
In general, a control is made so that the filter coefficient is updated in accordance with a far-end input signal and a near-end input signal after echo component cancellation. It is conventionally known that noise such as a bias (DC offset) in a far-end input signal makes it impossible to update the filter coefficient, thereby degrading the echo cancellation capability.
A non-patent document 1 discloses technologies related to active noise control instead of the echo canceller. It seems that the technologies are related to bias compensation of the adaptive filter and can be applied to the echo canceller.
Non-patent document 1: Nomoto, et al., “A Study on the Bias Compensation and the Variable Step Size Algorithms for the Filtered-X”, Technical Report of IEICE, DSP97-14 (1997-05)